Guide bars used for mounting saw chain on mechanical tree harvesters are typically provided with an oil receiving hole and an inner channel that carries the oil from the hole to the bar edge groove. Saw chain entrained on the bar edge includes a center link tang that extends into the groove. Oil is picked up by the center link and centrifugal force spreads the oil over the various bearing surfaces (the tangs sliding in the groove, the links turning on the rivets, the relative sliding of the overlapping links).
The greatest need for the lubrication is at the outer or nose end of the bar and on that side edge of the bar where cutting takes place. A tree harvester bar normally cuts crossway through a standing tree and in the cutting operation has a leading edge and a trailing edge. Typically a saw chain travels from the drive sprocket at the pivot end of the bar along the trailing edge of the bar, around the bar nose and back to the drive sprocket along the leading edge of the bar. The cutting operation takes place along the leading edge of the bar where the chain is traveling from the bar nose at the outer or free end of the bar to the drive sprocket at the inner or pivot end of the bar.
The oil hole that receives the oil under pressure is located at the pivot end of the bar, adjacent the trailing edge. In a conventional bar, a channel directly conveys the oil from the oil hole to the bar edge groove, i.e., at the point where the chain begins its non-cutting travel along the trailing edge toward the nose. The oil is carried along the full reach of the bar before it is applied to the high pressure area at the nose and back along the leading edge where the cutting takes place.
The oil is centrifugally thrown from the bar continuously during the travel of the chain around the bar. Accordingly much of the oil is lost before it reaches the cutting area. In a subsequent development, the bar was improved by rerouting the channel and extending it lengthwise along the bar interior to the bar nose. The oil was thus applied at the beginning of the high pressure area and was far more efficiently utilized in the cutting operation.
However, tree harvesters are not always operated in the abovedescribed typical fashion. For example, trees are often harvested in the winter and in climates where the trees are laden with snow and ice. The typical operation results in the saw chain drawing snow from the tree trunk into the motor mount housing. This causes problems and the snow has to be frequently cleaned out of the housing. Thus, operators of tree harvesters in winter conditions will often reverse the direction of travel of the saw chain. They still cut along the leading edge of the bar but the chain travels in a direction from the drive sprocket to the nose along this leading edge. This helps keep the housing free of snow and ice. However, the oil deposited at the bar nose is carried from the bar nose to the drive sprocket, along the non-cutting trailing edge, around the drive sprocket and then to the leading edge whereat the cutting takes place. The highest area of wear is the last to receive the oil. Furthermore, tests have shown that the chain travelling around the drive sprocket throws off a high percentage of the oil and a relatively small amount remains on the chain to lubricate the leading cutting edge.